Lubricating grease



Patented Mar. 4, 1952 LUBRICATIN G GREASE Rosemary olialloran, Elizabeth, and John J. Kolfenbach, Somerville, N. J., assignors to Standard Oil Development Company, a corporation of Delaware No Drawing. Application August 26, 1949, Serial No. 112,644

7 Claims.

This invention relates to a lubricating grease composition which has improved structural stability due to the presence of a selected range of fatty acid constituents.

Recent developments in grease technology have indicated an increasing need for greases of smooth structure which will provide satisfactory lubrication over a wide range of temperature conditions. It is desirable that such greases should also possess water resistance properties and high dropping points. It is widely recognized that these properties are to be found in mixed base greases, for example soda-barium greases, and in lithium greases. These greases are customarily prepared from their respective soaps of saturated fatty acid mixtures. Lithium and sodium-barium soaps can be dispersed in high V. I. oils and are therefore suitable as thickening agents in greases required to operate under widely varying temperature conditions, which is of special interest in the aeronautical field. In general, soaps are more difficult to disperse in high V. I. oils and greases employing high V. I. oils are subject to loss of structure upon extended working.

It is an object of this invention to provide a lubricating grease composition which is satisfactory for the lubrication of metal surfaces over a wide range of temperature conditions, and which has superior structural stability toward mechanical working.

It has now been found that the molecular weight distribution of the fatty acids employed in making these greases has a marked influence on their structural stability. This invention, therefore, comprises a lubricating grease composition which employs as the soap constituent a metal salt or a mixture of metal salts of substantially saturated fatty acids, the composition of the acid mixture being controlled so as to have a preferred molecular weight distribution.

For manufacturing grease compositions having the optimum structural stability, the mixture of fatty acids employed should contain 50% or more by weight of a single substantially saturated aliphatic acid having a carbon chain length within a range of from 16 to 22 carbon atoms and about 10% to about 30% by weight of a single saturated aliphatic acid having a carbon chain length 4 carbons fewer than the major component, that is to say, having a carbon chain length within the range of from 12 to 18 carbon atoms. The mixture of acids can, of course, have a certain amount of acids other than the two principal acids just described.

It is to be recognized, that the description of the fatty acids may be varied. For instance, since the molecular weight varies directly with the chain length, the preferred distributions may be expressed in terms of molecular weight ranges. In using this terminology the mixture of acids employed may be described as containing 50% or more of a substantially saturated aliphatic acid having a molecular weight range of 256 to 340 and from about 10% to 30% by weight of a substantially saturated aliphatic acid having a molecular weight within a range of 200 to 284.

The optimum combination of acids necessary to achieve structural stability may be arrived at by proper combination of commercially available fatty acids of well defined molecular weight distribution. For this application the various hydrogenated fish oil acids are not well suited. The molecular weight spread of the fatty acids in these mixtures vary markedly, since these acids represent distilled cuts of mixtures of acids containing variable amounts of C12 to C22 acids. The hydrogenated tallow acids, however, represent a fixed distribution, containing only C15 and C18 in essentially constant ratio. Employing a major proportion of an acid of fixed molecular weight distribution and a smaller proportion of an acid to provide the desirable distribution ensures more reproducible distribution. In the cases cited below, this was accomplished by the use of commercial myristic acid or hydrogenated sperm oil acids, which consist principally of myristic and lauric acids. It will be obvious that many other combinations are possible, such as a mixture containing 50 to 90% of pure palmitic acid, and 10 to 30% of lauric acid. Another example is behenic acid which is prepared by hydrogenating rape oil acids, and therefore contains about to behenic acid, and 10 to 15% stearic acid. However, the use of pure fatty acids to obtain the desired mixture is prohibitively expensive, so that the combination of hydrogenated tallow acids and hydrogenated sperm oil acids is to'be preferred. These acids possess the narrowest molecular weight range of available commercial acid mixtures. This mixture of acids is actually somewhat less expensive than the special fractionated hydrogenated fish oil acids. By the use of this acid mixture the molecular weight distribution of the total mixture is fixed, since in the preparation of the mixture, aproximately 72% of acids of a definite molecular weight range distribution are employed. a

' As an example of the application of this invention, and not to limit it in any way, several greases of the soda-barium (mol ratio 17/1) type were prepared according to the following general formula and method of manufacture.

EXAMPLE I The barium hydroxide was added in wa--' ter) to a mixture of the fatty acids and the" coastal distillate at 150 F. The mixture was stirred for minutes. j The sodium hydroxide in water) was then added, and the mixture was dehydrated. The Panhandle distillate was added,,the mixture heated to 400 F. and a sample taken for free acidity. The free acidity (A. S. T. M. D12S-47 Method) was adjusted to 0.4% as oleic acid, the phenyl alpha-naphthylamine was added and the grease was panned in 5-inch layer. After cooling for 10-16 hours, the grease cake was transferred to the A. S. T. M. motorized grease worker and the penetration after 60,000 strokes with the fine hole worker plate was determine-d as a measure of structure stability (345-350 mm./10, A. S. T. M. penetration on the cooled grease after an additional 60 strokes with the coarse hole plate being, considered borderline) The molecular weight distribution of the acids employed was varied either by selecting commercial acids of determined distribution, or by mixing acids of known molecular weight distribution. The acids employed, the molecular weight distribution in terms of number of carbons in the acid, and thestabilityof the greases to-mechanical working. are shown in Table I.

TABLE I 4 length of 16 carbon atoms or above. This is shown by Examples 1 and 2 wherein a high concentration of C12 and C14 acids did not produce any grease structure. In addition to the required higher molecular weight portion, however, it is necessary to have a minor amount of lower molecular weight material. Examples 3, 4, and 5 contain appropriate amounts of the desirable higher molecular weight constituents, but lack the lower weight material. A very broad range of molecular weights, illustrated by Examples 6, '7, and 8 are shown'to be the least desirable of all. Therefore, for optimum results the f tty acidsemployedshould be concentrated in molecular weight about a single molecular weight species, not less than C16 and preferably 018, but should contain a 'minor proportion, i. e. from 10% to 30% by weight, of an acid having an average chain length of about 4 carbon atoms fewer than the chain length of the acid present in the largest amount. In other words, theipreferred embodiment of this invention 'contem-- plates employing a mixture of fatty acids where-- in from to 90% by weight'of the mixture has an average carbon chain length of from Clfi'tO C22, and from 10 to 30% of an acid having a carbon chain length within a range of from C14 to C18- Examples 9, 10, 11, and 12 illustrate the preferred greases. dropping point within the range of 325-340 F.

In addition to the utility of this invention in mixed base soda soap greases, it has also been shown that a controlled mixture of fatty acids will effect an improvement in the shear stability ofv lithium soap greases. Two greases were prepared according to this general formula and method of manufacture.

EXAMPLE II 13.9% by weight, Fatty acids (saturated) 2.2% by weight, LiOH. H2O

0.5%. by weight, Phenyl alpha naphthylamine 83.4% by weight, phenol extractedcoastal distillate (Vis. at 210 F./45 SUS) Effect of molecular weight distribution on structural stability [Na/Ba Grease Containing 16% Soap in Mineral Oil Base Stock Molecular Weight Distribution P t t no 00 ene ra ion mm. 0 x Fine EIole-Plate 1 C12 C14 016 Cu C20 C22 Ex. l. Myristic Acid 3 6.1 89. 7 3. 7 .Q Doesnot disperse in oil. Ex. 2 Hydrofcl 30 Acids 4 U1. 24. 9 37. 6 30. 6 3. 4 Do. Ex. 3. Hydrofol Acids 51 HO 1.. 15.8 56.6 20.4. 3.4 1. 2 350. (Marginal). Ex; 4 Hydrofol Acids 405 1.2 20.4, 76.8 348 (Margmal). Ex. 5 Stearic Acid 55.0 45.0 361 (Unsatisfactory). Ex. G'Hydroiol Acids 53 5 7. 3 31. 0 23.7 21.8 12.0 365.(Unsat1sfactory). Ex. 7 Hydrofol Acids A B l. 7 13. 3 16.9 37.4 28. 4 370 (Unsatisfactory). 8 233%???1 3.0 45. e 12. 2 38.4 Fluid (Unsatisfactory). 72. 8 Bfgli-fiicdAcifi l1. 7 87.0 310 (Satisfactory).

x. l y rofo ci s405 E f g g a 0.6 10.1 18.7 69.0 305.

1:..11. 0 y roo Aci S405 E 12 MiyristigAfclid 65... 6

11. 0 yroo cis4 l r 0% Hydmm 3 Acids 4 5 -Blend of 85% by weight of a phenol extracted Panhandle distillate havin a viscosity at 2'0 F. of 44 S. U. S.

and 15% by weight of a phenol extracted coastal distillate having a viscosity at 210 F. of 37 S. U. 8..

viscosity index of the blend is 92.

The

. Penetration taken after grease cooled to room temperature and was workedan additional 60 strokes with large hole plate.

Commercial grade. 4 Hydrogenated sperm oil fatty acids. Hydrogenated fish oil fatty acids. MElydrogenated tall'ow acids.

These data indicate thatia' high percentage of a single molecular weight acid is desirable The acid was mixed with A; of the total amount of the base 'oil, heated to F. and the lithium providing that the single acid has a carbon chain 75 hydroxide was added as a boiling water solu- These greases have ation. 'rhe'mixtureifwas. dehydrated, oiled back, and ,was heated until a temperature of 400 F. was reached. The phenyl alpha naphthylamine was added and the mixture was pan cooled in a' 4 inch cake. The free acidity was found to be 0.06%,calculated as oleic acid (A. .S. T. M.

B128 4? Method) The first of these lithium greases was made with a commercially available hydrogenated fish oil acid (Hydrofol 51 HO) which is widely used in lithium soap grease manufacture. The second grease was made from a mixture of acids. The mixture was formualted according to the concept of this invention, and was one of the mixtures which gave optimum results in the case of the soda-barium grease. It had a dropping point in the neighborhood of 380 F. The acids employed, the molecular weight distribution in terms of the number of carbons in the acid, and the stability of the grease to mechanical working are shown in Table II.

TABLE II important feature of the invention i that the mixture of acids be distributed largely around a single molecular weight with a minor amount of acids of .a molecular weight about 56 units less than the molecular weight of the acid present in predominant amount.

What is claimed is:

1. A lubricating grease composition which con sists essentially of a lubricating oil thickened to a grease consistency with from 10 to 210% of a mixture of the sodium and barium salts of a mixture of substantially saturated aliphatic acids, said mixture of acids containing from 10 to 90% by weight of an acid in the C16 to 022 range and from 10 to by weight of an acid having 4 less carbon atoms than the acid present in the predominant amount.

2. A lubricating grease composition which consists essentially of a lubricating oil thickened to a grease consistency with a mixture of the sodium and barium salts of a mixture of substantially Effect of molecular weight distribution on structural stability [Lithium Grease Containing 15% Soap in Mineral Oil Base Stock Molecular Weight Distribution P t U [m 100 000 ene ra 011, mm Mixture 1: Fine Hole Plate 3 Cu 014 Cu Gm 020 C22 Example 1:

Hydrofol Acids 51 H0 15.8 56.6 20.4 3.4 1.2 Semi-fluid. lg ll 1A id 405 y r00 c s +30% flyd ofol 3 Acids a 1 Phenol extracted coastal distillate of SUS/Zlt) F. viscositv and 70 viscosity index.

These data indicate that a grease formed from the lithium salts of a mixture of acids having controlled molecular weight distribution prepared according to the concept of this invention is of excellent stability.

It will be understood by those familiar with the art that the soap content of greases will vary widely depending upon the consistency desired, the presence of additives and the nature of the lubrieating base oil. The examples cited above contain about 15% soap, but this is in no way limiting on the invention, since superior greases can be prepared using from 5 to soap providing the optimum fatty acid molecular weight distribution is maintained.

In summation, this invention comprises the manufacture of improved lubricating grease compositions which have excellent lubricatin qualities within a wide range of temperatures and, in addition which are not subject to loss of structural stability under prolonged conditions of shear. The grease compositions are made using salts of alkaline earth metals or alkali metals, or mixtures thereof, of substantially saturated aliphatic acids, said acids containing 50% to 90% of a single acid having from 16 to 22 carbon atoms and from 10% to 30% of another single acid having from 12 to 18 carbon atoms. It is to be understood, of course, that the mixture of acids can contain a certain amount of acids which do not fall in either of these categories. However, the

grease cooled to room temperature and was worked additional 60 strokes with large saturated aliphatic acids, said mixture of acids containing from 50 to 75% by weight of a 01s acid and from 10 to 30% by weight of a C14 acid.

3. A lubricating grease composition according to claim 1 in which the mixture of acids contains from 15 to 25% by weight of an acid having 16 carbon atoms.

4. A lubricating grease composition according to claim 1 in which the mixture of acids contains from 1 to 10% of an acid having 12 carbon atoms.

5. A lubricating grease composition according to claim 1 in which the mixture of acids contains substantially no acid having more than 18 carbon atoms.

6. A lubricating grease composition according to claim 1 in which the mixture of acids is a. commercial behenic acid.

7. An improved lubricating grease composition having a superior structural stability which consists essentially of a mineral base lubricating oil thickened to a grease consistency with the sodium and barium salt of a mixture of substantially saturated fatty acids, said mixture of acids having the following molecular weight distribution:

and containing incorporated therein 0.4% by weight of'phenyl alpha naphthylamine.

ROSEMARY OHALLORAN. JOHN J. KOLFENBACH. 1,

- 5 2,229,042 REFERENCES CITED 2,245,702

The following references are of record in the me ofthis patent:

"UNITED STATES PATENTS Name Date- Adams et a! Jan. 21, 1941 Brunstrum et a1. Jan. 21, 1941 Brunstrum et a1. Jan. 21, 1941' Morway 'June 17, 1941, 

1. A LUBRICATING GREASE COMPOSITION WHICH CONSISTS ESSENTIALLY OF A LUBRICATING OIL THICKENED TO A GREASE CONSISTENCY WITH FROM 10 TO 20% OF A MIXTURE OF THE SODIUM AND BARIUM SALTS OF A MIXTURE OF SUBSTANTIALLY SATURATED ALIPHATIC ACIDS, SAID MIXTURE OF ACIDS CONTAINING FROM 10 TO 90% BY WEIGHT OF AN ACID IN THE C16 TO C22 RANGE AND FROM 10 TO 30% BY WEIGHT OF AN ACID HAVING 4 LESS CARBON ATOMS THAN THE ACID PRESENT IN THE PREDOMINANT AMOUNT. 